The present invention provides polyols that are obtainable by a simple process. The invention further provides the process itself and also the use of the polyols according to the invention in the production of polyurethane materials.
Polyols suitable for the production of polyurethane materials such as flexible or rigid foams or solid materials such as elastomers are generally obtained by polymerisation of suitable alkylene oxides on polyfunctional starter compounds, that is to say starter compounds containing a plurality of Zerewitinoff-active hydrogen atoms. A very wide variety of processes has long been known for carrying out such polymerisation reactions, some of which processes complement one another:
On the one hand, the base-catalysed addition of alkylene oxides to starter compounds having Zerewitinoff-active hydrogen atoms is important on a large scale; on the other hand, the use of double metal cyanide compounds (“DMC catalysts”) for carrying out this reaction is becoming increasingly important. With the use of highly active DMC catalysts, which are described, for example, in U.S. Pat. No. 5,470,813, EP-A 700 949, EP-A 743 093, EP-A 761 708, WO 97/40086, WO 98/16310 and WO 00/47649, it is possible to prepare polyether polyols with very low catalyst concentrations (25 ppm or less), so that it is no longer necessary to separate the catalyst from the finished product. However, such catalysts are not suitable for the preparation of short-chained polyols or of polyols based on amino-group-containing starters. The basic catalysts which have long been known, for example those based on alkali metal hydroxides, permit the problem-free preparation of short-chained polyols and/or of polyols based on amino-group-containing starters, but the catalyst must generally be removed from the crude alkaline polymer by means of a separate working-up step. In the case of the preparation of amino-group-containing polyols in particular, yellow to yellowish-brown coloured products are frequently obtained; coloured starting materials are undesirable for certain applications, for example in the case of lacquers and coatings. The (Lewis) acid-catalysed addition of alkylene oxides to suitable starter compounds is of lesser importance.
The base-catalysed addition of alkylene oxides, such as, for example, ethylene oxide or propylene oxide, to starter compounds having Zerewitinoff-active hydrogen atoms is carried out, as has already been mentioned, in the presence of alkali metal hydroxides, but alkali metal hydrides, alkali metal carboxylates, alkaline earth hydroxides or amines such as, for example, N,N-dimethylbenzylamine or imidazole or imidazole derivatives can also be used. In the case of amino-group-containing starters having Zerewitinoff-active hydrogen atoms bonded to nitrogen atoms, up to one mol of alkylene oxides can be added per mol of Zerewitinoff-active hydrogen atoms without catalysis; if that ratio is exceeded; one of the above-mentioned basic catalysts must generally be added. When the alkylene oxides have been added, the polymerisation-active centres on the polyether chains must be deactivated. Various procedures are possible therefor. For example, neutralisation can be effected with dilute mineral acids such as sulfuric acid or phosphoric acid. The strength of the second dissociation stage of sulfuric acid is sufficient for the protonation of the alkali metal hydroxides formed by hydrolysis of the active alcoholate groups, so that 2 mol of alcoholate groups can be neutralised per mol of sulfuric acid used. Phosphoric acid, on the other hand, must be used in an equimolar amount relative to the amount of alcoholate groups to be neutralised. The salts formed in the neutralisation and/or during the removal of the water by distillation must generally be separated off by means of filtration processes. Distillation and filtration processes are time- and energy-intensive and, in addition, are not readily reproducible in many cases. Many processes have therefore been developed which can be carried out without a filtration step and, in many cases, also without a distillation step: Neutralisation with hydroxycarboxylic acids such as, for example, lactic acid is described in WO 98/20061 and US-A 2004167316 for the working-up of short-chained polyols for rigid foam applications; these are widely used and well established processes. U.S. Pat. No. 4,521,548 describes how the polymerisation-active centres can be deactivated in a similar manner by reaction with formic acid. The metal carboxylates formed after neutralisation with hydroxycarboxylic acids or formic acid dissolve to give a clear solution in the polyether polyols. However, a disadvantage of these processes is the catalytic activity of the salts that remain in the products, which is undesirable for many polyurethane applications. In WO 04/076529, the polymerisation reactions are therefore carried out with low catalyst concentrations of from 10 to 1000 ppm KOH, so that the catalytically active hydroxycarboxylic acid salts that remain in the polyol after the neutralisation are likewise present in a low concentration and accordingly are less disruptive for subsequent reactions. In JP-A 10-30023 and U.S. Pat. No. 4,110,268, aromatic sulfonic acids or organic sulfonic acids are used for the neutralisation; those acids likewise form salts which are soluble in the polyether polyols but are less basic and are distinguished by low catalytic activity. A critical disadvantage here is the high cost of the sulfonic acids. Working-up by means of acidic cation exchangers, as is described in DE-A 100 24 313, requires the use of solvents and their removal by distillation and is accordingly also associated with high costs. Phase separation processes require only a hydrolysis step and not a neutralisation step and are described, for example, in WO 01/14456, JP-A 6-157743, WO 96/20972 and U.S. Pat. No. 3,823,145. The phase separation of the polyether polyols from the alkaline aqueous phase is assisted by the use of coalescers or centrifuges; it is often necessary to add solvents here too in order to increase the density difference between the polyether phase and the aqueous phase. Such processes are not suitable for all polyether polyols; in particular, they are not successful in the case of short-chained polyether polyols or polyether polyols having high ethylene oxide contents. The use of solvents is cost-intensive, and centrifuges require a high outlay in terms of maintenance.
In the case of amine-catalysed alkylene oxide addition reactions, further working-up can be omitted provided that the presence of the amines in the polyols does not interfere with the production of polyurethane materials. Only polyols having comparatively low equivalent weights can be obtained by amine catalysis; see in this connection, for example, Ionescu et al. in “Advances in Urethane Science & Technology”, 1998, 14, p. 151-218.